For example, Patent Documents 1 and 2 disclose a wireless power supply system that supplies electric power from a storage battery mounted on an underwater mobile object to a storage battery installed in an underwater facility in a wireless manner. Recently, a wireless power supply system in which electric power is supplied in a wireless manner under water or on surface of water to a storage battery installed in a mobile object such as a working robot, which works while moving under water or on surface of water, has been proposed.
The term “wireless” in such a wireless power supply system means that an electric power transmission wire of a power-supplying device does not directly contact with an electric power transmission wire of a power-receiving device, and does not mean that a mobile object on which one of the power-supplying device and the power-receiving device is mounted is not in contact with a structure on which the other of the power-supplying device and the power-receiving device is mounted. In order to stably transmit electric power, it is desirable that the positional relationship between the power-supplying device and the power-receiving device be fixed. Accordingly, as disclosed in Patent Documents 1 and 2, the mobile object and the structure are firmly fitted and fixed to each other during the transmission of electric power.